Monday, July 25, 2016

A look back at power data

With the Tinman race being moved back a week to make room for Tropical Storm Darby I accepted an invitation from Ben Williams to check out his Computrainer set up at his new shop, Hawaii Triathlon Center. Very sweet, indeed. The task sort of simulated what we would have done for the race, only on a flat course and only thirty minutes. A thirty second time trial sounds deceptively easy. Without any let up by way of cornering or climbing or going downhill the legs just keep cranking out continuous power, something our bodies by nature dislike.

The first I saw reviewing my data was how my power level fell off. Actually it starts out a bit low, then shoots up, then falls. What happened there is that I began at an effort I planned to use cruising on the flat sections of the race course, then at Ben's urging changed to an all-out effort like that of a Lactate Threshold Heart Rate or CP30 test. After all, that is the definition of CP30, an all-out thirty minute time trial.

The second thing I noticed was how flat my heart rate was, once my power had settled down. Sure enough, I was grinding along at 140 BPM, exactly what my bike LTHR has been for at least a year. I was not paying attention to that number up on the display. I did notice I was hitting HR zone 5 on my Edge 800 head unit. My reaction to that was "Hey I am working pretty hard here." My attention was on the watts and cadence and trying to get both number higher. My legs refused to go faster for any length of time, and the HR line shows why. The body cannot sustain an effort above LTHR for very long. The more you do, the more it will cost a bit later.

Having gotten this far I decided to compare these numbers with some other recent data, with an eye on Honu. This turned up something quite revealing. My perceived effort at Honu was that I could not produce the power I needed. I felt like I was working really hard, but my speed and power numbers were well below plan. Take a look at this table and take note of the Honu numbers.

Date

Event

HR

PWR

% FTP

VI

CAD

7/23

Computrainer

140

134

81

1.01

74

7/19

Tantalus

135

139

84

1.04

44

6/4

Honu

137

96

58

1.19

68

5/15

Honolulu Tri

133

115

69

1.02

81

5/8

Ford Island TT

133

161

97

1.03

57

For each event I selected a section from the entire event.that represented a similar effort. For the Computrainer workout that was the middle, thirty minute time time minus the thirty minute warm up and cool down. For the Tantalus climb it begins just after the first turn and goes almost to the top, to where the pitch flattens out. For Honu it is from Kawaihae (sea level) to the top of the Hawi climb. This year's Honolulu Triathlon was flat and my goal was to ride it at 85% FTP, as practice for Honu. I missed that goal, probably because I never let my power go above 85 but it did drift below quite a bit. On Ford Island I had to stop in the middle for flag raising, so I used the second half.

Two things jump out at me. First, I could only average 96 watts on the Honu climb, and that was at a heart rate higher than plan. Yes, that is how I felt, unable to produce the power I knew I was capable of. Second, I do much better climbing at a low cadence than going fast on a flat road. On the Computrainer I should have been up at 166 watts, my FTP, since I was at my LTHR. Only hitting 134 tells me my legs need to be conditioned to produce power at high cadence.

Back in January I measured my FTP at 161. As you can see, the May test had it at 161, but right after that Training Peaks bumped it to 164, and two weeks ago it bumped me up again to 166. I suspect that those increases come mostly from the Tantalus rides.

One more thing. That column labeled "VI." That stands for variability index, a computed value that shows how much the entries in a data set vary. The set 140, 140, 139, 140 will have a VI near 1.0, while a set like 140, 135, 145, 140 will have a similar average but a higher VI. All of my VI numbers are good except for Honu. To me that suggests how much I was struggling trying to go faster.